Simple New Energy Converter Could Address Cost Issues for Wave Power

3 July 2008

Simulation of an Anaconda device in the sea. Click to enlarge.

Engineers at the University of Southampton (UK) are embarking on a program of large-scale laboratory experiments and mathematical studies to try to advance the development of a simple wave energy converter concept that promises wave-generated electricity at lower cost. The project is supported with more than £430,232 (US$852,233) in funding from the Engineering and Physical Sciences Research Council (EPSRC), and is in collaboration with the inventors and the developer of the device.

Called the Anaconda, the device is a large distensible rubber tube that is closed at both ends and filled with water. It is designed to be anchored just below the sea’s surface, with one end facing the oncoming waves.

A wave hitting the end squeezes it and causes a bulge wave to form inside the tube. A bulge wave is a wave of pressure produced when a fluid oscillates forwards and backwards inside a distensible tube. The bulge wave travels at a speed that is determined by the geometry and material properties of the tube.

Inside the tube, the bulge waves are accompanied by a periodically reversing flow. One way of extracting power from the Anaconda is to use a pair of duck-bill valves to convert this into a rectified flow past a turbine between high and low pressure reservoirs. Power produced is fed to shore via a cable.

Because it is made of rubber, the Anaconda is much lighter than other wave energy devices (which are primarily made of metal) and dispenses with the need for hydraulic rams, hinges and articulated joints. This reduces capital and maintenance costs and scope for breakdowns.

The Anaconda was invented by Francis Farley (an experimental physicist) and Rod Rainey (of Atkins Oil and Gas). Their website on the Anaconda is at http://www.bulgewave.com. Manufacturing rights for the Anaconda now belong to Checkmate SeaEnergy, part of the Checkmate Group.

The Anaconda concept has only been proven at very small laboratory-scale, so questions about its potential performance still need to be answered. Using tubes with diameters of 0.25 and 0.5 meters, the University of Southampton experiments will assess the Anaconda’s behaviour in regular, irregular and extreme waves.

Parameters measured will include internal pressures, changes in tube shape and the forces that mooring cables would be subjected to. As well as providing insights into the device’s hydrodynamic behaviour, the data will form the basis of a novel mathematical model that can estimate exactly how much power a full-scale Anaconda would produce.

The mathematical studies undertaken by the EPSRC-funded project are novel because the Anaconda’s response to pressures induced by surface waves is much more complex than that of a ship or an offshore structure. It has many more degrees of freedom, and motions of each kind (vertical and horizontal bending, bulging, stretching, ovalling, twisting) all interact because of the compliant nature of the rubber.

When built, each full-scale Anaconda device would be 200 meters long and 7 metres in diameter, and deployed in water depths of between 40 and 100 meters. Initial assessments indicate that the Anaconda would be rated at a power output of 1MW (roughly the electricity consumption of 2,000 UK houses) and might be able to generate power at a cost of 6p (US$0.12) per kWh or less. Although around twice as much as the cost of electricity generated from traditional coal-fired power stations, this compares very favorably with generation costs for other leading wave energy concepts.

A one-third scale model of the Anaconda could be built next year for sea testing and we could see the first full-size device deployed off the UK coast in around five years’ time.

—Professor John Chaplin, leader of the EPSRC-funded project

The Anaconda is one of the new concepts identified by the Carbon Trust’s Marine Energy Accelerator initiative as having potential to deliver breakthrough reductions in the cost of energy.

Together with tidal energy, it is estimated that wave power could supply up to 20% of the UK’s current electricity demand.

Comments

Typically a rubber tube filled with water will bulge locally when squeezed; and this bulge will propagate along the tube at a speed c given by

C =sqrt(Eh/dp)

Here E is the tensile modulus of the rubber, d the diameter of the tube, h its wall thickness and dp is the density of water. You can control the speed by choosing the dimensions of the tube and the properties of the rubber.

Young's modulus (E) in GPa for rubber is 0.01-0.1.
For steel, it is 190-210.

To increase the speeds of the wave in the linear direction reinforce the rubber/plastic with imbedded steel wire longitudinally along the length of the tube.

This reinforcement will reduce the amount of rubber/plastic required to contain the bulge wave.

In addition, the tension of the steel reinforcing cables could be adjusted by microprocessor controllers to optimize the bulge wave propagation over a wide range of wave conditions. It is doubtful that this optimization strategy has been considered in this early stage of the tube design.

If variable (ie instantly changing output) generation aggregates to about 20% of the grid, the grid itself becomes very unstable and subject to oscillations.

To damp the effect, an enormous amount of spinning reserve must be on-line to stabilize the network or blackouts will occur over the entire net, collapsing the entire grid.

So in addition to being costly to install, the cost must be doubled for enormous amounts of idling hot reserve, that is not used but still consumes energy and capital.

For example if you need 20% more power, you cannot satisfy that with just installing 20% of so-called renewables that are variable (and also possibly intermittent), you must also install 20% of idling spinning reserve for example coal, gas, nuclear or hydro power too; to stabilize the grid.

Then if the renewable is also intermittent(predictable off line) like solar, that works only during daytime, then you must plan for the intermittent times when it predictably won't be available at all. As well as the variable output for cloudy days. You could handle that with other base load power, say coal, nuclear, geothermal, or hydro, but that adds even more cost.

This was not recognized at first by the chuckle-heads, who can only comprehend: "Wind, sun good;, others bad!".

This information is the result of experience painfully relearned, with using so called renew-ables in operations, in Sweden, the Netherlands and Denmark.

EEs are not surprised about grid stability issues; but the magnitude of handling it is a surprise. As the grid EEs don't have much experience with constantly variable and intermittent power sources comprising so much of the grid, with their constantly shifting power production.

Historically, grid oscillations are prevented and handled by predictable power additions/losses in large amounts, as plants come online and offline with sufficient reserves to handle potential problems. They handle instantaneous variable demand fluctuations, but statistically small and insignificant; when compared to the grid reserves, by small amounts of spinning reserve. Stability issues were relatively, easy to handle.

Now grid instability is presenting real problems.

Contributing to the problem is that utility commissions have numbers of phony, demagogic so-called utility commissioners who get elected by "saving customers money".

They do this by denying requests to build new "unnecessary" plants, thereby reducing the rate base; but shaving off grid reserve margins,at a time when they need to be larger than ever.

Of course, this only delays the day of reckoning, and with variable and intermittent renewables both present and in growing amounts, exacerbates grid stability problems, enormously.

The typical eco know-nothing, or his self-appointed political leaders being poli-sci, P/Jornalsim majors or lawyers, they wouldn't understand "Imaginary power flows" sloshing about a grid, if it rose up and bit 'em in the arse.

It will. And it has.

Hey dumkomps, there was a reason our forefathers abandoned variable, and intermittent power sources, back when. They couldn't handle the associated problems.

And no, it wasn't an evil scheme, by the "Big Water", "Big Coal", "Big Gas", "Big Oil", or later "Big Nuclear" interests, creating a CONSPIRACY.

As the current Left tries to tear down every institution of excellence or competence, in Society. Or deflects the blame for the predictable, "unintended" (like this one), consequences of their own gross stupidity.

Wow, anon., quite a tirade! Grid instability is clearly an issue. The UK had a couple of nukes close down just the other week and it caused, apparently, no end of problems.

I know people on both sides of the house who are for or against increasing renewable generation capacity. It serves neither side to turn the debate into a political one. The questions, surely, are what is needed and what can feasibly be done to achieve what needs to be achieved.

Will, it was large coal facilities that were offline, due in no small part to the European LCPD, that caused the blackouts last month.

The LCPD creates an perverse incentive to plant operators to NOT run their power plants unless the electricity prices are high enough to warrant it, so the large base load (coal) plants are trying to stay offline and only fire up at peak time to make the most of their allowances.

Expect more moaning about the LCPD as blackout increase in frequency. Expect to see it widely ignored if the blackouts are bad enough.

Nukes had nothing to do with last months outage, although in the long run, the UK does have issues with nuclear capacity.

The answer to mitigating grid fluctuations is broadening the local grid to a regional, or even better, national grid.

When the grid is large, time zone energy consumption behavior evens load out over the day. Many intermittent power sources also average to a base load character if the number and type of power sources is broad enough.

This grid broadening should be accomplished using HVDC for high efficiency power distribution. In the US, this can be accomplished though the right leadership at the federal level to override petty local concerns; grated at the current time that leadership is lacking and must be fixed.

In Europe, the EU should consider a continent wide grid to average this intermittent power production profile.

Hmm, while the article is about a wave capture device - this discussion seems to be about frustration over denial- of-build licenses. And variable power sources. These wave capture devices are only rated at 1MW annually. Hardly a big contribution to grid resource at this stage. And as the article suggests, the power may simply be put to use pumping water into reservoirs - a relatively stable power source.

Wind power does provide baseload and fortunately provides somewhat more power during day time when demand is higher.
www.stanford.edu/group/efmh/winds/aj07_jam.pdf

The problem with nuclear is that it is extremely expensive, depends on ridiculous subsidies and provides full power at night when demand is low and thus requires load leveling from hydro power plants.
www.npr.org/templates/story/story.php?storyId=89169837
www.npr.org/templates/story/story.php?storyId=15545418

As for as the concern about intermittent power coming from renewables the wave concept has to be one of the most consistent out there. It will certainly need some buffering but the waves don't start and stop on a dime like the sunlight does. Wave energy increases over usually days and decreases over the same time from. Seas don't often go from 10 foot waves to 2 foot waves in a matter of a couple of hours.

That said energy storage does need to be boosted to make way for more renewable energy and wave technology would be one of the least likely to cause blackouts due to quick changes in power output.

@Ben,
Beleive it, The trend towards more efficient lighting, two person houeholds (average) and more careful energy accounting will see the 500W figure as quite adequate. Not everyone has electric heating and hot water. That would cerainly compromise this figure.
Since NO ONE talks electric space and water heating from renewables, this is not a problem.

Current household electricity consumption in The Netherlands is now at around 3500 kWh per year. That's way less than 500 W average. This provides a standard of living that I believe is comparable to that in the UK.

I live in The Netherlands, and the last power failure I have experienced is at least 20 years ago (although there were failures in other regions but that was not due to renewables). Stan, please show me the reports about these disasters that never happened.

HOUSTON (Reuters) - A drop in wind generation late on Tuesday, coupled with colder weather, triggered an electric emergency that caused the Texas grid operator to cut service to some large customers, the grid agency said on Wednesday.

Electric Reliability Council of Texas (ERCOT) said a decline in wind energy production in west Texas occurred at the same time evening electric demand was building as colder temperatures moved into the state.

The grid operator went directly to the second stage of an emergency plan at 6:41 PM CST (0041 GMT), ERCOT said in a statement.

I hope previous comment "no one expects space and water heating be met by renewables literally. Most of us know that solar water and air(space) heaters are very viable conditioning is balanced by photovoltaic and of course geothermal, hydro including pumpstorage can provide useful base load levelling.
If the accelerated move to renewables proceeds with due care we should expect the appropriate enabling technologies to cover the expected and unforeseen problems.
We will necessarily learn more as we go.

Short term stability in Ontario I've noticed is solved by raising and lowering the incoming 110vac by +/-10%.
Which I assume is some kind of demand management technique like 'brownouts'.

The Utilities are also offering incentives to wire up our residential A/C to a device which the Power Authority can then use to turn off the cooling at times of peak demand. Such controls added to domestic electric hot water heaters as well may cause minimal impact on lifestyles but would assist the utility from having to buy power at the highest rates during peak periods.

Obviously the Authority hasn't heard of a device that's even more effective at cooling - it's called a WINDOW.

And for correspondents who may wonder at the 500W average power by British residents whether it be caused by lack of attention to our personal hygene. While it doesn't bode well for someone who can't even spell the word correctly, I can assure readers that in England we are all in the habit of taking a shower at least once a month WHETHER WE NEED IT OR NOT !
T2

"If variable (ie instantly changing output) generation aggregates to about 20% of the grid, the grid itself becomes very unstable and subject to oscillations ....[blah blah blah blah]... As the current Left tries to tear down every institution of excellence or competence, in Society. Or deflects the blame for the predictable, "unintended" (like this one), consequences of their own gross stupidity."

Apart from the inanity of your rant at the end, your post is hopelessly inaccurate. I suggest you read the DoE report "20 Percent Wind Energy by 2030: Increasing Wind Energy's Contribution to U.S. Electricity Supply":

http://www1.eere.energy.gov/windandhydro/pdfs/41869.pdf

20%. Huh. What do the DoE know?

And that's just "evil" wind power. Now integrate all the other, vast, renewable resources which are available to us using a continental scale grid and what do we have?

Renewable energy is very important nowadays especially that the traditional energy sources are getting used up. It's a good thing if there will be more number of investments for it.http://www.refillenergy.com